Process for improving the mechanical characteristics of objects consisting of beryllium or beryllium alloy



United States Patent 3,350,241 PROCESS FOR IMPROVING THE MECHANICAL CHARACTERISTICS OF OBJECTS CONSISTING 0F BERYLLIUM 0R BERYLLIUM ALLOY Jos Mallen, Paris, and Michel Weisz, Orsay, France, as-

signors to Commissariat a IEnergie Atomique, Paris, France No Drawing. Filed Oct. 1, 1964, Ser. No. 400,902 Claims priority, application France, Oct. 10, 1963, 950,126 1 Claim. (Cl. 148-115) The present invention relates to a process for improving the mechanical characteristics of objects consisting of beryllium or beryllium alloy.

It is known that beryllium is a metal which is generally employed for the production of alloys. It is also used to produce casings for fuel elements of nuclear reactors.

Under the operating conditions of such a use, it is im portant to improve the mechanical characteristics of this metal and notably its elastic limit at elevated temperature and its ductility.

The present invention concerns a thermo-mechanical treatment which produces an improvement.

The process according to the present invention is characterised in that there is imparted to the object, which is brought to a temperature close to its recrystallisation tem-' perature, a low permanent deformation, generally below that of the critical cold Working at this temperature, for a period such that there is obtained a considerable relief of the initial internal stress resulting from the imparted deformation, whereafter the object is allowed to cool.

The deformation may be imparted particularly by trac tion, compression, torsion or bending.

The above defined thermo-mechanical treatment produces a change in the structure of the metal and in its mechanical characteristics.

By way of example, there will be mentioned an application of the process to beryllium sheet whose initial characteristics, determined by tensile tests, are the following where E is the elastic limit of the metal and A is the ductility of the metal expressed as relative extension:

Temperatgre test E 0.2 kgJmm. A, percent 3,350,241 Patented Oct. 31, 1967 It will be seen on comparing the two foregoing tables that the ductility of the metal treated is increased throughout the temperature range and is quintupled at 600 C. The value of the elastic limit at 600 C. is doubled in relation to that of the original metal.

It is to be noted that the aforesaid complete stress relief phase is an essential condition of the treatment. If this condition is not satisfied, the characteristics of the metal are not modified.

The treatment according to the invention is applicable to various structural states: rough extruded or rolled state, whether recrystallised or not, with or without preheating treatment.

The treatment according to the invention may be industrially applied to various products and in particular to tubes intended for the production of casings for nuclear reactors.

In particular, it may be used for straightening rough cold worked tubes. This straightening may be effected by traction applied under the following conditions:

(a) The stress applied must involve an imparted deformation, for example, 'by means of a screw system, and not an imparted force;

(b) The temperature and duration conditions depend only upon one factor: production of complete relief of the initial tension;

(c) The deformation to be imparted in this case will be a compromise between that necessary for straightening the tube and the optimum deformation determined in each particular case by preliminary tests.

We claim:

A process for improving the mechanical characteristics of sheets, bars and tubes of beryllium and beryllium alloys comprising the steps of heating them to a temperature approaching the recrystallization temperature of about 600 C., then applying a low permanent deformation of approximately 0.2% thereto below that of critical cold working for this temperature for a period of approximately 15 minutes whereby a considerable relief of the initial internal stress resulting from the imparted deformation is obtained and then cooling them.

References Cited FOREIGN PATENTS 5/=1961 Great Britain. 2/ 1963 Great Britain.

OTHER REFERENCES DAVID L. RE'CK, Primary Examiner. H. F. 'SAITO, Assistant Examiner. 

